Sialon has a structure in which aluminum and oxygen are dissolved in silicon nitride. In general, there are two types of crystal systems of sialon, namely, α-sialon and β-sialon that belong to a hexagonal crystal system. Sialon-based sintered bodies containing such sialon have a characteristic of low reactivity with metals and have been developed as materials for cutting tools. Recently, there have been developed sintered bodies containing cubic sialon, which has higher hardness than α-sialon and β-sialon, in order to increase hardness and to improve wear resistance when the sintered bodies are used as cutting tools (Patent Literature 1).
There have been developed sintered bodies further containing, in addition to cubic sialon, cubic boron nitride (hereinafter referred to as “cBN”), which has high hardness second to diamond, in order to further increase hardness and to further improve wear resistance when the sintered bodies are used as cutting tools (Patent Literature 2). Cutting tools that include such a sintered body containing sialon and cBN exhibit good wear resistance in machining a difficult-to-cut material such as Inconel (trademark of Special Metals Corporation), which is a nickel-based heat-resistant alloy.